In response to this funding opportunity announcement, our research group proposes to integrate the measurement of physical activity and food intake in "real-time" with newly developed methods in geospatial data management and analysis (Geographic Information Systems [GIS]), to address research questions related to energy balance and obesity. We introduce the multi-sensor board (MSB), cutting-edge, nonobtrusive technology capable of capturing diverse cues from a variety of sources during physical activity, including acceleration, elevation (barometric pressure), audio, light, and geophysical location. We will further exploit the unique movement and location sensing capabilities of the MSB to determine the location and frequency of eating episodes, and we will couple this information with a custom nutrition program that we will develop that will allow participants to record the type and amount of foods they consume at the time of eating. Thus, we will measure movement through space and time, under truly free-living conditions, to examine relationships between the major lifestyle behaviors related to energy balance and obesity -- namely physical activity and food intake -- and the built environment. The primary aims of this exploratory/developmental study are to develop and validate our novel approaches to measuring energy expenditure and energy intake. Another innovative aspect of the study is that this information will be integrated into a cellular telephone, which will be programmed to provide continuous feedback to the user in terms of increasing energy expenditure through increased physical activity and better utilization of locations and land uses that are associated with physical activity. The purpose of this third study aim is to explore the potential use of the integrated MSB-cellular telephone platform as a personal assistive device that could be used to monitor energy expenditure, energy intake, and energy balance in real-time to facilitate behavior changes favorable to weight loss or weight control.